Replace deprecated 'compile' gradle configuration with 'implementation' (react-native-image-picker#1010)

According to [[email protected]](https://github.com/react-native-community/react-native-releases/blob/master/CHANGELOG.md#057) default gradle version is now `4.4`.

Author: hyochan

android/build.gradle

@@ -51,15 +51,15 @@ repositories {
 }
 
 dependencies {
-    compile "com.facebook.react:react-native:+"  // From node_modules
+    implementation "com.facebook.react:react-native:+"  // From node_modules
 
-    testCompile "junit:junit:4.10"
-    testCompile "org.assertj:assertj-core:1.7.0"
-    testCompile "org.robolectric:robolectric:3.3.2"
+    testImplementation "junit:junit:4.10"
+    testImplementation "org.assertj:assertj-core:1.7.0"
+    testImplementation "org.robolectric:robolectric:3.3.2"
 
-    testCompile "org.easytesting:fest-assert-core:${FEST_ASSERT_CORE_VERSION}"
-    testCompile "org.powermock:powermock-api-mockito:${POWERMOCK_VERSION}"
-    testCompile "org.powermock:powermock-module-junit4-rule:${POWERMOCK_VERSION}"
-    testCompile "org.powermock:powermock-classloading-xstream:${POWERMOCK_VERSION}"
-    testCompile "org.mockito:mockito-core:${MOCKITO_CORE_VERSION}"
+    testImplementation "org.easytesting:fest-assert-core:${FEST_ASSERT_CORE_VERSION}"
+    testImplementation "org.powermock:powermock-api-mockito:${POWERMOCK_VERSION}"
+    testImplementation "org.powermock:powermock-module-junit4-rule:${POWERMOCK_VERSION}"
+    testImplementation "org.powermock:powermock-classloading-xstream:${POWERMOCK_VERSION}"
+    testImplementation "org.mockito:mockito-core:${MOCKITO_CORE_VERSION}"
 }